1. Field of the Invention
The present invention relates to an LCD (liquid crystal device) operated by thin film transistors as active matrix switching elements, and particularly relates to a semiconductor device for a flat liquid crystal display and method of making the same.
This application is based on Patent Application No. Hei 9-302579 filed in Japan, the content of which is incorporated herein by reference.
2. Background Art
Recently, thin film transistors (TFT) are being widely used as active switching elements for driving liquid crystal flat display devices. Among those thin film transistors, a forward stagger type configuration, in which a gate electrode is mounted on the upper side of a channel layer, and source and drain electrodes are mounted in the lower side, is advantageously used because of its simple structure, and reduced number of lithographic steps in manufacturing, and such that the manufacturing cost is low.
An example of the representative forward stagger type TFT is shown in FIG. 5. The TFT is provided with, on an insulating substrate such as a glass plate, a metallic light shielding film 3, a transparent interlayer insulating film 4, a pixel electrode 12, a source electrode 5, a drain electrode 6, an n+ amorphous silicon layer 7, an amorphous silicon layer 8, a gate insulating film 9, a gate electrode 10; and the TFT is covered and protected by a protective insulation film 13. The source electrode 5 and drain electrode 6 are formed on a pixel electrode 12 and a residual layer 14 made of the same material as that of the pixel electrode, and the drain electrode 6 is connected to the pixel electrode 12 through the residual layer 14.
A practical example of an active matrix panel is disclosed in Japanese Patent Application, First Publication No. Hei 7-239481, in which, as shown in FIG. 5, an n+ amorphous silicon 7 is separated into the source electrode 5 side and the drain electrode 6 side.
In this forward stagger type TFT, it is necessary to provide a formation process of a light shielding film, in order to suppress the leak current caused by the light admittance to the amorphous silicon layer 8.
In contrast, in a TFT disclosed in Japanese Patent Application, First Publication No. Hei 9-92618, a black matrix normally formed by a Cr film at the color filter side is mounted at the TFT substrate side, concurrently with the formation of the light shielding film.
Japanese Patent Application, First Publication No. Hei 5-210119 has proposed an active matrix liquid crystal display screen, in which the black matrix and the color filter are formed under the forward type stagger TFT, concurrently with the formation of the light shielding layer.
In the conventional forward stagger type TFT, a photolithographic process is needed for forming the light shielding film, so that, it is difficult to reduce the number of manufacturing processes, and it is not advantageous to adopt such TFT for flat type display devices for which cost reduction is required.
As disclosed in the above mentioned prior art references, when the black matrix is formed at the color filter side, it is necessary to precisely align the black matrix with the TFT substrate, that is, the black matrix must be overlapped accurately with the TFT substrate. For this reason, it is necessary but difficult to increase a so-called aperture which corresponds to expanding the area of the pixel electrode.
It is therefore an object of the present invention to provide a semiconductor device and a method of manufacturing the same, which is particularly suitable for a flat display LCD operated by an active matrix display principle using the a-SiTFT, and which has an increasing aperture, and a reduced manufacturing cost by reduction of the number of manufacturing processes.